This invention relates generally to dynamoelectric machines such as large turbine generators and particularly to such machines that have an air gap baffle assembly for controlled leakage of a gas coolant from the air gap.
Background reference is made to Calfo et al. U.S. Pat. No. 4,315,173, Feb. 9, 1982, which discloses a machine with an air gap baffle assembly in which the baffle ring is formed from a plurality of arcuate segments to enable access to the rotor assembly by removal of one or only a small number of segments. Also, Calfo et al. U.S. Pat. No. 4,118,645, Oct. 3, 1978, discloses a dual position air gap baffle assembly with one position used in operation of the machine and another used to provide an opening for rotor access.
Air gap baffle ring assemblies are used to regulate the flow of cooling gas through the air gap of large machines. A number of forms of baffle assemblies have been employed successfully but have required considerable maintenance, which is desirably to be minimized. Generally such baffle assemblies are secured to the stator core or stator end turns. By their inherent nature they reduce the effective air gap. One difficulty has been that the location of the air gap baffle assembly may cause it to be easily struck by the generator rotor when the rotor is installed within the stator. If that occurs, ties binding the baffle assembly to the stator end turns may be broken or stretched. Some assemblies have a neoprene rubber seal attached to the baffle ring which extends into the air gap. If the assembly is dislocated by any movement, the rubber seal may contact the rotor and be destroyed, thus losing effective control of the gas flow. More cooling gas would flow down the air gap causing other parallel gas paths to the stator windings, stator core, parallel rings, and bushings to receive less gas flow and hence the temperatures of those components would rise undesirably. Also, the debris generated by a rubbing seal is capable of damaging blower and cooler components, as well as blocking small ventilation passages in the stator windings and core.
Therefore, upon any damage to the rubber seal, its replacement was necessary. Removal of the entire air gap baffle ring assembly is generally required to replace the seal. With this type of seal it is very difficult to maintain a specified air gap, because of seal variations.
A previous improvement was made to air gap baffle assemblies that involved the use of a resin-filled hose in addition to rope ties for securing the baffle assembly on the stator winding. Such assemblies were favorable in providing slightly more space to install the rotor since the baffle ring is on a larger diameter, on the stator winding rather than the core, and also provided more support to hold the ring in position if hit by the rotor during installation. A better seal between the baffle ring and the stator windings is also provided by the resin-filled hose.
With the addition of radial vents in the core step iron, better control of the clearance between the rotor retaining ring and the air gap baffle assembly was required to maintain effective cooling. Air gap baffle assemblies were formed which contained a notch out for the rotor skid pan. The rotor skid pan is a partial cylindrical element placed over the bottom of the stator bore during installation of the rotor. The baffle assembly rotated 90.degree. to allow the installation of the skid pan. After installing the rotor and removing the skid pan, the ring was rotated 90.degree. and inner baffle rings with a rubber seal between them was installed. The difficulty with this system is that the rubber seal still varies and can contact the rotor. Also, the rotating assembly uses steel hardware which is heated by the high flux in the area.
The present invention avoids the need for a rubber seal ring for the ultimate definition of the clearance. This is favorable because rigid ring members define a more accurate gap. However, it remains the case that it is highly desirable to configure air gap baffle assemblies in improved ways so as to provide greater ease of installing the rotor with less likelihood of damage to the baffle assembly, whether or not a flexible seal is used. The present invention does so.
One aspect of the invention is that the baffle assembly includes a resin-filled hose on the stator winding to support the air gap baffle ring in the axial direction and to provide a seal on the outer diameter of the assembly to the stator core. The air gap baffle ring is supported on and tied to the stator winding. The air gap baffle ring is sometimes referred to herein as the "outer ring". It is the ring element furthest out from the center of the generator bore. The outer ring is machined concentric to the generator bore on its outer diameter or outer surface. However the inner surface or inner diameter of the outer ring is machined eccentric to the generator bore so that the thickest section of the ring is at the upward or 12 o'clock position while the thinnest section is at the downward or 6 o'clock position. This permits installation of the skid pan without rotation of the ring or any inner rings and also eliminates the need for metallic hardware. The rotor skid pan is then installed and the rotor is installed. After removal of the skid pan, inner rings of the air gap baffle ring assembly are installed. Each inner ring is a full circle ring with an eccentric outer diameter. and a concentric inner diameter. The eccentric offset matches the offset in the air gap baffle outer ring. Thus, the inner ring is installed with the thinnest cross-section at the 12 o'clock position and the thickest cross-section at the 6 o'clock position. The result is that the inner diameter of the inner ring determines the final gap and can be made reliably uniform.
In preferred forms of the invention, two inner rings are used, one axially in front of the other with a locking ring in between and glass bolts through in front and rear rings. In this way the inner rings are made secure while permitting their easy removal in the event of rotor removal or their reinstallation after rotor replacement. Consequently, the arrangement of an air gap baffle assembly with eccentric surfaces on the inside of an outer ring and the outside of an inner ring yields a durable baffle ring assembly and one that is suitable for easy installation and removal.